Nacaduba cyanea, the tailed green-banded line-blue, is a species of butterfly in the family Lycaenidae, and formerly considered a member of the genus Danis. It is found in the Indonesia (Irian Jaya, Maluku), Papua New Guinea, the Solomon Islands and Australia (Queensland). The wingspan is about 30 mm. Adult males are blue with a dark brown wing margin, with a pale blue to white patch on the hindwing. Females are white, with a black border around the wings and a row of blue-edged black spots.